A ligament is a piece of fibrous tissue which connects one bone to another.
Ligaments are frequently damaged (e.g., detached or torn or ruptured, etc.) as the result of injury and/or accident. A damaged ligament can impede proper motion of a joint and cause pain.
Various procedures have been developed to repair or replace a damaged ligament. The specific procedures used depend on the particular ligament which is to be restored and the extent of the damage.
One ligament which is frequently damaged as the result of injury and/or accident is the anterior cruciate ligament (ACL). The ACL 2 extends between the top of the tibia 4 and the bottom of the femur 6 (FIG. 1). A damaged ACL can cause instability of the knee joint and cause substantial pain and arthritis.
Numerous procedures have been developed to restore the ACL through a graft ligament replacement. In general, these ACL 2 replacement procedures (FIG. 2) involve drilling a bone tunnel 8 through the tibia 4 and up into the femur 6. Then a graft ligament 10, consisting of a harvested or artificial ligament or tendon(s), is passed through the tibial tunnel 12, across the interior of the joint, and up into the femoral tunnel 14. Then a distal portion of the graft ligament is secured in the femoral tunnel 14 and a proximal portion of the graft ligament is secured in the tibial tunnel 12.
There are currently several different ways to secure a graft portion in a bone tunnel. One way is to use an interference screw 16 (FIG. 2) to aggressively wedge the graft ligament against the side wall of the bone tunnel. Another way is to suspend the graft ligament in the bone tunnel with a suture 18 (FIG. 3) or a cross-pin 20 (FIG. 4). Still another way is to pass the graft ligament completely through the bone tunnel and affix the ligament to the outside of the bone with a screw and washer arrangement 22 (FIG. 2) or a staple (not shown).
Depending on the fixation device and its manner of use, some fixation will occur at the portion of the bone tunnel nearest to the interior of the joint, and some fixation will occur intermediate the bone tunnel or adjacent to the portion of the bone tunnel farthest from the interior of the joint. For example, an interference screw 16 set into the femur 6 will typically be positioned substantially adjacent to the interior of the joint 26 (FIG. 5); however, an interference screw 16 set into the tibia 4 will frequently be positioned relatively far from the interior of the joint 26 (FIG. 6). On the other hand, suture 18 (FIG. 3) and cross-pin 20 (FIG. 4) suspensions will typically effect securing intermediate the length of the bone tunnel or at the far end of the bone tunnel, and screw and washer fixations 22 (FIG. 2) will typically effect securing relatively far from the interior of the joint 26.
It has been observed that whenever the graft ligament is secured remote from the interior of the joint 26 (i.e., in the middle of the bone tunnel or adjacent to an outer surface of the bone), the graft ligament 10 will be relatively unsupported at the point where the ligament 10 passes from the bone tunnel into the interior of the joint. As a result, as the knee flexes back and forth through its natural range of motion (FIG. 7), the graft ligament moves about within the mouth 28 of the bone tunnel, rubbing against the walls of the bone tunnel. Over time, this can cause damage to the graft ligament and the wear down the mouth 28 of the bone tunnel, both to the serious detriment of the patient. It can also result in enlargement of the entire tunnel diameter, e.g., as shown at 30. Less than a tight fit may result in incursion of synovial fluid into the tunnel, which is hypothesized to contribute to the tunnel-widening phenomenon.